1.3 2D and 3D shapes
‘2D’, or ‘two-dimensional’, simply means that the shape is flat. We can draw 2D shapes on paper. Common examples are shown in Figure 5.
A ‘3D’ (‘three-dimensional’) shape is a solid shape. It has three dimensions, that is, length, width and depth. An easy way of thinking about the difference between a 2D and a 3D shape is to think ‘If I shone a torch on the shape, would it have a shadow?’ 3D shapes cast a shadow but 2D shapes don’t.
Obviously the screen that you’re reading this on is 2D, so 3D shapes are represented using shading.
Activity 3: 2D or 3D?
Say if the following shapes are 2D or 3D:
Which shapes in Figure 7 are 2D and which are 3D?
Answer
Shapes (a), (c) and (e) are 2D.
Shapes (b), (d) and (f) are 3D.
OpenLearn - Everyday maths 1 (Northern Ireland) 
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